Color gamut is an index for describing the color fidelity that a display can achieve. At present, the back-light solution, employed in the industry to excite the quantum dot material by blue light to generate white light, may achieve 100% of NTSC (National Television Standards Committee) color gamut.
In the prior art, quantum dots of different sizes may be excited by irradiation of the blue light to release red light and green light of high purity, which are then mixed with the remaining pure blue light to obtain white light of high brightness. At present, when quantum dots are applied to a direct or bottom-type display, a back-light module in the industry employs a method of coating quantum dots on a diaphragm, and its specific structure is as shown in FIG. 1: a light-emitting chip 102 is arranged on a back plate 101, and blue light emitted from the light-emitting chip 102 is irradiated onto a diaphragm 103 coated with quantum dots so that the quantum dot material on the diaphragm 103 coated with quantum dots can be excited to emit red light and green light of high purity. In this solution, since the entire diaphragm 103 needs to be coated with the quantum dot material, the usage amount of the quantum dots is relatively large, resulting in relatively high cost of this solution.
In order to solve the problem of high cost, another solution in the industry is to arrange quantum dots above an LED (Light Emitting Diode) chip as point light sources. FIG. 2 schematically shows a structure diagram of a back-light module employing such point light sources. As shown in FIG. 2a, a plurality of point light sources 202 are arranged on a back plate 201. Each point light source 202, the structure of which is as shown in FIG. 2b, includes an LED chip 202a, and a quantum dot layer 202b arranged above the LED chip 202a. In this way, the usage amount of quantum dots is saved.
However, the light intensity of the LED chip 202a in each point light source 202 shows Lambertian distribution, i.e., a unit area having a smaller light-emitting angle of the LED chip 202a results in higher light power, and the power of light in a unit area having a small angle, irradiated onto the quantum dot layer 202b, may reach 60-100 W/cm2. As shown in FIG. 2b, the light power received by a region of the quantum dot layer 202b directly facing the LED chip 202a is higher than that received by a region diagonally opposite to the LED chip, and the temperature of a region in the quantum dot layer receiving high light power is higher than the temperature of a region in the quantum dot layer receiving low light power. Since the failure of the quantum dot material will be caused at high temperature, the limit of irradiation of blue light that the quantum dot layer may withstand is generally below 5 W/cm2. Therefore, the quantum dot layer 202b right above the LED chip 202a is more likely to be irradiated by blue light of high intensity, resulting in the failure of the quantum dots.